Michelle Oliver and Amanieu d'Antras
Topic 7.2: Radioactive Decay 7.2.1 Describe the Phenomenon of Natural Radioactive Decay The nucleus of an atom can become unstable, meaning it has too much energy and wants to get rid of it. This is due to the number of protons and neutrons in the nucleus. ·Neutrons hold the protons together but are not themselves stable and will decay if isolated. If there are too many neutrons then they become isolated from protons and can thus decay. ·If there are not enough neutrons then the protons will repel each other and result in an unstable nucleus. ·If there are too many protons (more than 83) the atom is not stable no matter how many neutrons are added. Natural radioactive day is a completely random process that is governed by the weak and nuclear force. It is a way for the unstable nucleus to lose energy and become more stable. There are three main types, alpha, beta, and gamma decay. 7.2.2 Describe alpha, beta and gamma radiation and their properties
Alpha Decay: the process in which the nucleus ejects an alpha particle which is a helium nucleus (2 protons 2 neutrons)
Example:
A
K1 ->
A-4
K2 +
4
α
Z
Z-2
2
Properties of radiation: Alpha particles do not penetrate very far, they tend to lose their energy quickly, making them not very dangerous to humans if the source is outside the body. However if the source is inside the body, like radon gas, it becomes very dangerous. Alpha particles have a large ionizing energy.
Beta Negative Decay: the process by which a proton decays into a neutron and a positron and emits an electron neutrino. The mass of the neutron is greater than the mass of the proton, therefore beta negative decay does not occur without an input of energy.
A
K1 -->
A
K2 +
0
e+ ν
Z
Z+1
-1
Beta Positive Decay: The process by which a neutron decays into a proton and an electron and releases and anti-neutrino.
A
K1 -->
A
K2 +
0
e+ v
Z
Z-1
1
Properties of Radiation: beta particles have a much greater penetration ability and are more hazardous to humans. They also have less ionizing energy than alpha particles.
Gamma Decay: The process by which an excited nucleus decays into a lower energy level. It releases a gamma ray.
K* -->
K +γ
Properties of Radiation: can penetrate easily and can ionize, dangerous to humans. 7.2.3. Describe the ionizing properties of radiation and its use in the detection of radiation The Geiger-Muller tube is an example of radiation detection devices. It is a tube filled with inert gas with a cathode and anode creating a strong electric field inside the tube. When the ionized radiation enters the tube it strips electrons off the gas molecules creating ions. The ions are accelerated by the electric field and create more ions, eventually creating a pulse of current which is detected
7.2.4 Outline the biological effects of ionizing radiation
7.2.5 Explain why some nuclei are stable while others are unstable.
7.2.6State that radioactive decay is a random and spontaneous process and that the rate of decay decreases exponentially with time.
7.2.7 Define the term radioactive half‑life.
Radioactive half-life is the amount of time needed for half of the particles in a substance to decay.
13.2.4: Describe β+ decay, including the existence of the neutrino.
energy + p+ → n0 + e+ + νe
β energy spectra are continuous, and that the neutrino was postulated to account for these spectra. 13.2.5: State the radioactive decay law as an exponential function and define the decay constant. Nt = N0e − λt
The decay constant is defined as the probability of decay of a nucleus per unit time. (http://en.wikipedia.org/wiki/Half-life) 13.2.6: Derive the relationship between decay constant and half-life. (http://en.wikipedia.org/wiki/Half-life) 13.2.7: Outline methods for measuring the half-life of an isotope. Measure the amount of substance at different points in time, the plot a graph and use it to determine the half-life (See 7.2.8). 13.2.8: Solve problems involving radioactive half-life.
Topic 7.2: Radioactive Decay
7.2.1 Describe the Phenomenon of Natural Radioactive Decay
The nucleus of an atom can become unstable, meaning it has too much energy and wants to get rid of it.
This is due to the number of protons and neutrons in the nucleus.
· Neutrons hold the protons together but are not themselves stable and will decay if isolated. If there are too many neutrons then they become isolated from protons and can thus decay.
· If there are not enough neutrons then the protons will repel each other and result in an unstable nucleus.
· If there are too many protons (more than 83) the atom is not stable no matter how many neutrons are added.
Natural radioactive day is a completely random process that is governed by the weak and nuclear force. It is a way for the unstable nucleus to lose energy and become more stable. There are three main types, alpha, beta, and gamma decay.
7.2.2 Describe alpha, beta and gamma radiation and their properties
- Alpha Decay: the process in which the nucleus ejects an alpha particle which is a helium nucleus (2 protons 2 neutrons)
Example:Properties of radiation: Alpha particles do not penetrate very far, they tend to lose their energy quickly, making them not very dangerous to humans if the source is outside the body. However if the source is inside the body, like radon gas, it becomes very dangerous. Alpha particles have a large ionizing energy.
Properties of Radiation: beta particles have a much greater penetration ability and are more hazardous to humans. They also have less ionizing energy than alpha particles.
Properties of Radiation: can penetrate easily and can ionize, dangerous to humans.
7.2.3. Describe the ionizing properties of radiation and its use in the detection of radiation
The Geiger-Muller tube is an example of radiation detection devices. It is a tube filled with inert gas with a cathode and anode creating a strong electric field inside the tube. When the ionized radiation enters the tube it strips electrons off the gas molecules creating ions. The ions are accelerated by the electric field and create more ions, eventually creating a pulse of current which is detected
7.2.4 Outline the biological effects of ionizing radiation
7.2.5 Explain why some nuclei are stable while others are unstable.
7.2.6 State that radioactive decay is a random and spontaneous process and that the rate of decay decreases exponentially with time.
7.2.7 Define the term radioactive half‑life.
Radioactive half-life is the amount of time needed for half of the particles in a substance to decay.
7.2.8 Determine the half-life of a nuclide from a decay curve.
(http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/HalfLife/halfLife.html)
7.2.9 Solve radioactive decay problems involving integral numbers of halflives.
- N0 is the initial quantity of the thing that will decay (this quantity may be measured in grams, moles, number of atoms, etc.),
- Nt is the quantity that still remains and has not yet decayed after a time t,
- t1 / 2 is the half-life of the decaying quantity,
(http://en.wikipedia.org/wiki/Half-life)13.2.4: Describe β+ decay, including the existence of the neutrino.
β energy spectra are continuous, and that the neutrino was postulated to account for these spectra.
13.2.5: State the radioactive decay law as an exponential function and define the decay constant.
Nt = N0e − λt
The decay constant is defined as the probability of decay of a nucleus per unit time.
(http://en.wikipedia.org/wiki/Half-life)
13.2.6: Derive the relationship between decay constant and half-life.
(http://en.wikipedia.org/wiki/Half-life)
13.2.7: Outline methods for measuring the half-life of an isotope.
Measure the amount of substance at different points in time, the plot a graph and use it to determine the half-life (See 7.2.8).
13.2.8: Solve problems involving radioactive half-life.